lp2985aim5-3.8 National Semiconductor Corporation, lp2985aim5-3.8 Datasheet - Page 14

• Manufacturer Part Number: lp2985aim5-3.8
• Description: Micropower 150 Ma Low-noise Ultra Low-dropout Regulator Designed For Use With Very Low Esr Output Capacitors
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Hints
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP2985 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.
Input Capacitor
An input capacitor whose capacitance is
between the LP2985 input and ground (the amount of capac-
itance may be increased without limit).
This capacitor must be located a distance of not more than 1
cm from the input pin and returned to a clean analog ground.
Any good quality ceramic, tantalum, or film capacitor may be
used at the input.
Important: Tantalum capacitors can suffer catastrophic fail-
ure due to surge current when connected to a low-impedance
source of power (like a battery or very large capacitor). If a
Tantalum capacitor is used at the input, it must be guaranteed
by the manufacturer to have a surge current rating sufficient
for the application.
There are no requirements for ESR on the input capacitor, but
tolerance and temperature coefficient must be considered
Turn-On Time
Turn-On Time
≥
1 µF is required
10014040
10014042
14
when selecting the capacitor to ensure the capacitance will
be
Output Capacitor
The LP2985 is designed specifically to work with ceramic out-
put capacitors, utilizing circuitry which allows the regulator to
be stable across the entire range of output current with an
output capacitor whose ESR is as low as 5 mΩ. It may also
be possible to use Tantalum or film capacitors at the output,
but these are not as attractive for reasons of size and cost
(see next section Capacitor Characteristics).
The output capacitor must meet the requirement for minimum
amount of capacitance and also have an ESR (equivalent se-
ries resistance) value which is within the stable range. Curves
are provided which show the stable ESR range as a function
of load current (see ESR graph below).
≥
1 µF over the entire operating temperature range.
Turn-On Time
10014041